An acoustic wave device employing a 42-degree rotated Y-cut lithium tantalite board is often used for a filter and an antenna duplexer of telecommunication equipment. In recent years, a high performance acoustic wave device having a preferable temperature characteristic is demanded. To realize the acoustic wave device, a silicon dioxide film is deposited on an IDT electrode on a lithium niobate piezoelectric substrate to improve the temperature characteristic. Particularly, an acoustic wave device using lithium niobate having a cut angle to make a Rayleigh wave as a main acoustic wave is expected to realize a high resonance Q.
In this acoustic wave device, however, spurious emission is produced since, for instance, a spurious emission is caused by a higher-order transverse mode signal and other spurious emission is caused by an unwanted wave signal other than the Rayleigh wave of the main acoustic wave, deteriorating a passband characteristic of a filter.
Japanese Patent Laid-Open Publication No. 2011-101350 describes a conventional acoustic wave device which suppresses spurious emissions caused by a higher-order transverse mode out of various spurious emissions.
This acoustic wave device suppresses the higher-order transverse mode spurious, but does not sufficiently suppress spurious emission caused by the unwanted wave signal other than the main acoustic wave signal.